RSpec and Api::CoursesController Tests

For Courses and Lessons..

* Created migrations for schema
* Created models for both at app/models/
* Added API endpoints for both at app/controllers/api
* Added Routes for both at config/routes.rb
* Added serializers for both at app/serializers

Project Wide..

* Added Serializer gem and initializer for it in config/initializers/serializer.rb
* Added Annotate gem. run annotate in the root to have it automatically add comments to the top of model files based on the schema.
* There's a bunch of other files, like stub tests, which are autogenerated by rails model/controller generators. Leave them for now, because we expect to use those exact files later on.